EP0534532B1 - Axle detector built in the surface of a multi-lane road - Google Patents

Description

The invention relates to an axle detector for installation on the surface of a multi-lane carriageway, including at least one piezoelectric coaxial cable comprising a central conductor, a metal sheath and a filling material between the sheath and the conductor.

The invention finds its application to the counting of vehicles on roads or motorways with several lines, for example 5 or more.

Three categories of axle detectors are already known from the state of the art.

The first category consists of visual detectors which are not reliable because on a multi-lane road, several vehicles can pass head-on and therefore hide from each other.

The second category consists of detectors simply placed on the road. In this category, there is for example the device described in patent application FR 2 625 808, which relates to a piezoelectric film strip. This kind of device has a life that is really too limited due to the fragility of the connection between the piezoelectric film and the cable for connection to the recording device which is generally available on the side of the road. In this category, there are also pneumatic tubes, which are also fragile, and which on the other hand cannot be active other than over their entire length, so that on a multi-lane road, one cannot distinguish the quantity traffic that affects each queue separately.

The third category consists of detectors buried in the roadway. In this category we finds for example the device described in patent application FR 2 575 827, which corresponds to US-A-4 712 423. This known device comprises, with reference to FIG. 3, in a groove made in a pavement, a layer of attachment to the walls of the groove, and, between a piezoelectric sensor and this layer, one or more resins enveloping the sensor. It also includes a metal profile, around the piezoelectric sensor, embedded in the filling materials.

It will be noted that the latter device uses a piezoelectric cable as the piezoelectric detector conforming to that described in patent FR 2 109 176.

The third category of devices have in common that they are mechanically resistant over time. So they can be permanently installed on a road. However, those who use resins for coating the piezoelectric sensors present temperature resistance problems when the climatic conditions of the region where they are installed vary.

If the devices falling into the third category seem a priori the only ones to present adequate performances, they nevertheless present in some cases a serious disadvantage: their installation in the road requires works which on the one hand deteriorate the road in a certain measure and which on the other hand are long to implement.

However, there is the problem of equipping with axle detectors, motorways or roads having several lines, for example 5 or more, which is a very common case in the United States of America.

The increase in road traffic worldwide is reflected in the creation of increasingly large motorways or roads, with a large number of lanes in each direction, and by a request from the authorities responsible for road transport, better knowledge of traffic; this as well for pavement design, for the improvement of traffic flow, than for the realization of automatic tolls.

Thus, when a highway is very busy with traffic, and has many lanes, it is practically impossible to be able to close it to traffic for the long enough time necessary for the installation of interred sensors of the third category mentioned, and this all the more so since, very often, only a punctual study of traffic is sufficient to gather the data necessary for the evaluation or better understanding of traffic. We must therefore use a detector placed on the road surface.

A detector to be placed on the surface of the road is also known from patent application FR 2 575 827, with reference to its figure 4. This device comprises a flat housing, 1 cm thick, having access ramps at a bevel , including a piezoelectric cable like that described in the same document for the buried sensor, disposed in a groove in this housing and held by a coating material.

The piezoelectric cable or detector known from patent FR 2 109 176 and used in patent application FR 2 575 827 both buried and on the surface, comprises a sheath and a central conductor made of titanium, and a piezoelectric filling material which is a mixture of titanate and lead zirconate, or barium titanate doped with lead titanate, and which is compacted between the sheath and the central conductor.

However, none of the known devices solves the problem posed by the use of an axle detector to be arranged in a simple manner on the surface of a multi-lane carriageway involving an extremely rapid installation, which is specially suitable to provide differentiated data for each of the lanes on this carriageway assumed to be heavily loaded with road traffic, even if these properties have as a counterpart that this installation is temporary, owing to the fact that the device has a relatively short lifespan, due to the traffic load, provided that this track duration is nevertheless long enough to allow data to be collected wanted.

• à poser en surface d'une chaussée à plusieurs voies,
• facile à fixer à l'emplacement choisi,
• perturbant le trafic ausi peu que possible lors de son installation, et ne le perturbant aucunement lors de son utilisation,
• ayant une durée de vie suffisant à collecter les données voulues, par exemple 1 semaine en trafic lourdement chargé,
• fournissant des données sélectives propres à chacune des voies de la chaussée, avec aussi peu d'interférences que possible avec les données considétées comme parasites provenant des autes voies,
• facile à raccorder à un dispositf d'enregistrement disposé sur le bas-côté de la chaussée, au moyen d'un dispositif de connexion mécaniquement aussi résistant dans le temps que le détecteur d'eessieux lui-même,
• ce détecteur excluant tout connecteur dans la partie exposée au trafic,
• ce détecteur ayant donc des parties aptes à être disposées sélectivement sur chacune des voies à étudier,
• ce détecteur étant par exemple apte à effectuer des mesures sur des chaussées aussi larges que 5 à 10 voies,
• ce détecteur étant en outre résistant aux conditions climatiques difficiles (très fortes ou faibles températures, variations brutales de températures, pluie, neige, verglas, etc...).

A technical problem which the invention proposes to solve is therefore to provide an axle detector for possibly temporary installation,

• to be installed on the surface of a multi-lane carriageway,
• easy to attach to the chosen location,
• disrupting traffic as little as possible during its installation, and not disturbing it in any way during its use,
• having a sufficient lifespan to collect the desired data, for example 1 week in heavily loaded traffic,
• providing selective data specific to each lane of the roadway, with as little interference as possible with the data considered as interference from other lanes,
• easy to connect to a recording device located on the side of the road, by means of a connection device mechanically as resistant in time as the axle detector itself,
• this detector excluding any connector in the part exposed to traffic,
• this detector therefore having parts capable of being selectively arranged on each of the channels to be studied,
• this detector being for example suitable for carrying out measurements on pavements as wide as 5 to 10 lanes,
• this detector also being resistant to difficult climatic conditions (very high or low temperatures, sudden temperature variations, rain, snow, ice, etc.).

The cable known from patent FR 2 109 176 is not suitable for solving this problem.

Indeed, it is known to those skilled in the art that the "filling" piezoelectric material is composed of particles or piezoelectric domains which, when the material is "raw" are distributed randomly. The raw material is therefore isotropic: each piezoelectric domain has its own orientation, so that the sum of the charges which can be created there is very small. The material really shows a usable piezoelectric effect only if the domains are oriented in a preferred direction. This is done, when making the piezoelectric cable, by applying an intense electric field to the material while bringing it to a temperature close to the Curie point. Such a manufacturing process is particularly described in said patent FR 2 109 176 already cited.

Thus, by means of this cable, a sensor can be obtained which is long enough, for example 20 m, to cross a 5-lane carriageway, but this cable does not provide differentiated information on the traffic relating to each of the lanes crossed.

On the other hand, such a piezoelectric cable has serious additional drawbacks. Indeed, piezoelectric cables are very capacitive, for example they have a capacity of the order of 10,000 pF / m. A 20 m long sensor made using such a cable would represent a capacity of 0.2 ”F. A capacitance of this order of magnitude is a drawback both if the collected signal is processed by a charge amplifier, since 0.2 "F is too large as the source impedance, as well as if the signal is processed by a voltage amplifier because the capacity lowers the voltage generated by the sensor in a ratio which can be greater than 5 for a 20 m sensor.

According to the invention, a solution is provided to all of these problems by means of a detector as defined in the preamble of claim 1, and further characterized in that it comprises at least one so-called active region where the filling material is piezoelectric and at least one adjacent region called neutral where the filling material is neither non-potentially piezoelectric nor piezoelectric.

In one implementation of the invention, the sheath is made of copper, the central conductor is made of copper, the piezoelectric filling material is a piezoelectric ceramic and the non-potentially piezoelectric filling material is a mineral powder insulator.

In a preferred implementation, the piezoelectric ceramic is chosen from a mixture of lead titanate and zirconate, or barium titanate doped with lead titanate, and the powdered mineral insulator is chosen from magnesia (MgO), silica (SiO₂) or alumina (Al₂O₃) or a mixture of several mineral insulators comprising, inter alia, one of these powders.

• la figure 1 représente un câble piézoélectrique en coupe transversale,
• la figure 2 représente un câble piézoélectrique en coupe longitudinale,
• la figure 3 représente un détecteur pour chaussée à plusieurs voies,
• la figure 4 représente, vu de dessus, un côté d'une autoroute à 5 files dans une direction de la circulation, entre le terre-plein central et le bas-côté.
• la figure 5 montre en coupe transversale une structure coaxiale fixée sur une chaussée par une bande adhésive après son enrobage dans un profilé ou un tube élastique,
• la figure 6 montre en coupe transversale la structure coaxiale simplement fixée sur une chaussée par une bande adhésive.

The invention is described below in detail with reference to the appended schematic figures, of which:

• FIG. 1 represents a piezoelectric cable in cross section,
• FIG. 2 represents a piezoelectric cable in longitudinal section,
• FIG. 3 represents a detector for multi-lane carriageways,
• Figure 4 shows, seen from above, one side of a 5-lane highway in a traffic direction, between the central reservation and the shoulder.
• FIG. 5 shows in cross section a coaxial structure fixed on a roadway by an adhesive strip after its coating in a profile or an elastic tube,
• Figure 6 shows in cross section the coaxial structure simply fixed to a floor by an adhesive strip.

As shown in longitudinal section in FIGS. 1 and 2 and in transverse section in FIG. 3, the axle detecting device 10 essentially comprises a coaxial structure formed by a central conductor 1, a metal sheath 2 and d a pulverulent filling material 3, 4 disposed between the central conductor 1 and the sheath 2.

The coaxial structure is made of a length L sufficient to cover one or more lanes of a multi-lane carriageway, for example to be used on a highway having between 2 and 10 lines. Thus, FIG. 4 represents, seen from above, one side of a 5-lane highway in a traffic direction, between the central reservation 100 and the shoulder 106.

In Figures 1 and 2, there is shown schematically respectively two implementations of the coaxial structure 10 suitable for the detection of vehicles traveling on the fifth line 101 counted from the aisle of the motorway, it being assumed that the device electronic recording 110 of the data collected is placed away from road traffic, on this highway shoulder 106 as shown in FIG. 4. In another use of the axle detector, the electronic recording device 110 of the data could instead be placed on the central reservation 100.

So with reference to FIGS. 1 and 2, the coaxial structure 10 has a length L capable of covering the 5 motorway queues, that is to say about 20 m. Parts A, B, C, D, E of the coaxial structure will correspond, after the installation of the axle detector across the highway, respectively to lines 101, 102, 103, 104 and 105 shown schematically in the figure 4.

For the detection of axles on the fifth row 101, only the part A of the coaxial structure 10 must be capable of piezoelectric effect and this piezoelectric effect must be radial, that is to say according to the radius of the device shown in section on FIG. 3. The other parts B, C, D etc., arranged between the line on which the measurements are carried out and the shoulder 106 of the motorway, must be neutral, and in particular must not emit parasitic signals coming from the passage of vehicles on lines 102 and 103, etc.

This is why, during the production of the coaxial structure 10, only the part A is provided with a potentially piezoelectric filling material 4. The other parts B, C, D, etc. have a completely neutral filling material 3.

The method for producing the coaxial structure 10 comprises forming a blank for the cable, the diameter of which can be 0.5 to 3 cm. The blank comprises the metal sheath 3, the central conductor 1 and the pulverulent filling materials 3 and 4 distributed over the length of the blank in the proportions of a part corresponding to A for the potentially piezoelectric material and four parts corresponding to B, C, D, E for the neutral material.

The blank is then subjected to drawing and rolling operations with annealing to bring it to the definitive diameter and length suitable to form the coaxial structure for the axle detector. In doing so, the powders are made compact in the different parts of the cable. The final diameter is between 1 and 3 mm, and the length in the case taken as an example of cable for 5 channels is of the order of 20 m.

As shown in longitudinal section in FIG. 1, each of the ends 51, 52 is sealed with a sealed insulating plug leaving a portion of the central conductor 1 protruding.

As shown in longitudinal section in Figure 2, at one end 54, the sheath 2 is completely closed, without contact with the central conductor 1 and at the other end is arranged a sealed insulating plug 53, leaving a part of the central conductor 1.

In both cases, one of the ends where the central conductor is available is provided with a coaxial connection socket which may for example be of the BNC type. Preferably the coaxial structure intended to make the axle detector is connected by this socket to a transmission cable, represented by the references 21, 22, 23, 24 and 25 in FIG. 4 and which is commercially available from THERMOCOAX (Suresnes -FRance) under the reference RG58 Cu.

Different examples of products for producing the different parts of the coaxial structure are given below.

EXAMPLE I

The central conductor can be made of copper as well as the external conductive sheath. Part A potentially piezoelectric can contain the pulverulent filling material chosen from piezoelectric ceramics already sold, for example PEX₅ from PHILIPS (Netherlands), from which a powder of the mixture of lead titanate and zirconate having a point is obtained Curie at 285 ° C. The neutral parts are favorably filled with a powdery mineral insulator chosen from magnesia MgO, silica SiO₂, alumina Al₂O₃.

EXAMPLE II

• un mélange de titanate et de zirconate de plomb ou de baryum,
• du titanate de baryum dopé avec quelques % de titanate de plomb par exemple 5 %.

The central conductor can be made of copper as well as the external conductive sheath. The potentially piezoelectric filling material of the active part A can be chosen from:

• a mixture of titanate and lead or barium zirconate,
• barium titanate doped with a few% of lead titanate, for example 5%.

If the potentially piezoelectric material contained only one titanate, it would be more easily depolarized, after its polarization.

EXAMPLE III

The central conductor and the metallic sheath can be made of metals other than copper, for example titanium. But titanium is expensive compared to copper. This is why we will rather look for a cheap metal, because the detector according to the invention is rather intended for temporary use, that is to say not reusable after the few days or about a week of installation in a given site.

EXAMPLE IV

It is also possible to use, with the conductor and the sheath in one of the metals of the preceding examples, filling materials chosen from polymers. Thus, for the potentially piezoelectric part A, it is possible to choose the filling material from PVDFs which are fluoropolymers commercially available from ATOCHEM (Elf-Aquitaine United States). For neutral parts B, C, D etc. we will then choose for example a polyethylene.

When the blank has finished being mechanically and thermally treated to provide the desired coaxial structure for application to the axle detector, it is subjected to the biasing operation of the potentially piezoelectric part. This operation consists in applying a high electric field to the coaxial structure, at the same time as the latter is brought to a temperature close to the Curie point of the piezoelectric material. For the application to axle detection, the polarization must be radial.

To this end, a DC voltage of appropriate intensity is applied between the sheath and the central conductor.

For the implementation of the various operations leading from the blank to the operational piezoelectric coaxial structure, a person skilled in the art can refer to the teaching of patent FR 2 109 176.

It is at this stage that the importance of differentiating the filling material 4 from the active part showing the piezoelectric effect is revealed, and the completely neutral filling material 3 from the other parts B, C, D, etc.

Indeed, if the coaxial structure was filled over its entire length, that is to say on all the parts as well as A, B, C, D, etc. of potentially piezoelectric material, and if, during manufacture, only the desired active part A was subjected to the polarization process, then the cable would have at least the following drawbacks.

On the one hand, a very high capacity, very harmful to the processing of the signal collected by a system 110 (see FIG. 4) including a signal amplifier as known to those skilled in the art for collecting information relating to road traffic.

On the other hand, parts B, C, D etc. that we want neutral would be very slightly sensitive although not having undergone the process of polarization. In this case it would be very difficult to differentiate between a spurious signal and an attenuated signal. By attenuated signal is meant a signal created by a light vehicle in the active part A, and by parasitic signal, a signal created by a heavy truck in one of the neutral parts B, C, D etc.

Figure 4 shows a schematic view from above of all the elements of a detector for a 5-lane highway.

This detector comprises a first coaxial structure 11, as described according to reference 10 in FIGS. 1, 2 and 3, for example having an active part A of approximately 3.5 m for applying across the line 101 furthest from the aisle 106, and having neutral parts B, C, D, E, of about 3.5 m each for applying across rows 102, 103, 104, 105. A coaxial connection cable referenced 21, connected to the end 53 by a coaxial connector not shown, transports the signals relating to the active part A to an input 31 of an electronic processing device 110. The connector, the connection cable 21, and the electronic device 110 are arranged at the traffic shelter on the roadside 106.

Obviously in another application, the device 110 could be placed on the central reservation 100 of the highway concerned and in this case the coaxial structure 11 would be arranged head to tail.

The detector then comprises a coaxial structure 12 of the same type as the structure 10 described above, having an active part A arranged across the fourth channel from the aisle in this example, and having only three neutral parts B, C, D straddling tracks 103, 104, 105. A connection 22 similar to what has been described previously connects the end 53 of the structure 12 to the inlet 32 of the device 110.

The detector further comprises structures respectively 13, 14, 15 each having an active part A, and respectively, two neutral parts B, C; a neutral part B, and no neutral part; and each having a connection cable respectively 23, 24, 25 to connect them to the inputs 33, 34, 35 of the device 110.

The external neutral parts, that is to say respectively E, D, C, B of the structures 11, 12, 13, 14 provided for crossing the line 105, may be longer than those which are intended to pass through the other parts, so as to allow the arrangement of the end 53 well outside of the traffic on the shoulder. Also the structure 15 which theoretically comprises only an active part A, can comprise a neutral part between the part A and the end 53 for this same reason.

The coaxial extension cables 21, 22, 23, 24, 25 can have a length of up to 20 m.

• a) Les structures coaxiales 11, 12, 13, 14, 15 présentent des capacités gênantes aussi faibles que possible : les parties neutres ne dépassent pas les valeurs de 300 pF/m avec la magnésie et 100 pF/m avec le polyéthylène. Cette diminution de la capacité représente une amélioration considérable par rapport au cas où l'on utilserait une structure comprenant sur toute sa longueur du matériau potentiellement piézoélectrique qui résulte en une capacité de 10 000 pF/m.
• b) Les signaux transmis, relatifs à chaque voie 101, 102, 103, 104, 105 ne sont pas affectés par la circulation sur les autres voies, du fait des parties ayant comme matériau de remplissage des produits complètement neutres.
• c) Toutes les connexions sont à l'abri de la circulation sur la bas-côté ou le terre-plein central ; il n'y a pas de connecteur sur la chaussée.
• d) Le détecteur peut s'appliquer à toute autoroute quel que soit le nombre de voies. Il suffit de réaliser, outre la partie active A, la longueur adéquate de parties neutres B, C, D, etc. On a déjà testé des structures pour des autoroutes à 10 files.
• e) Chaque partie, active ou neutre, peut être prévue de la longueur appropriée à l'application choisie, les autoroutes à équiper pouvant avoir des voies plus ou moins larges, notamment à l'emplacement des péages.
• f) Chaque structure peut être fixée sur la chaussée très rapidement, en interrompant la circulation pendant un minimum de temps.
• g) Les structures coaxiales 11, 12, 13 etc ont été testées sur autoroutes très chargées en circulation. Elles ont une durée de vie de l'ordre de 1 semaine en moyenne, ce qui est en général suffisant pour réaliser une étude du trafic. Elles peuvent avoir une durée de vie beaucoup plus longue dans un trafic plus léger ou moins rapide.
• h) Les structures coaxiales sont très bon marché. Donc elles peuvent être considérées comme temporaires, à une seule utilisation, ou jetables.

The advantages provided by a detector composed of the elements described above are the following:

• a) The coaxial structures 11, 12, 13, 14, 15 have annoying capacities as low as possible: the neutral parts do not exceed the values of 300 pF / m with magnesia and 100 pF / m with polyethylene. This reduction in capacity represents a considerable improvement compared to the case where a structure comprising over its entire length potentially piezoelectric material would be used, which results in a capacity of 10,000 pF / m.
• b) The signals transmitted, relating to each channel 101, 102, 103, 104, 105 are not affected by traffic on the other channels, due to the parts having as filling material completely neutral products.
• c) All connections are protected from traffic on the shoulder or the central reservation; there is no connector on the road.
• d) The detector can be applied to any highway regardless of the number of lanes. It suffices to carry out, in addition to the active part A, the appropriate length of neutral parts B, C, D, etc. We have already tested structures for 10-lane highways.
• e) Each part, active or neutral, may be provided with the appropriate length for the chosen application, the motorways to be equipped may have more or less wide lanes, in particular at the location of tolls.
• f) Each structure can be fixed to the road very quickly, interrupting traffic for a minimum of time.
• g) The coaxial structures 11, 12, 13 etc have been tested on heavily loaded motorways in circulation. They have a lifespan of around 1 week on average, which is generally enough to carry out a traffic study. They can have a much longer lifespan in lighter or slower traffic.
• h) Coaxial structures are very inexpensive. So they can be considered temporary, single use, or disposable.

Two methods of fixing structures 11, 12, 13, etc. are given below by way of example, across the road, with this viewpoint of inexpensive and short-use axle detectors, or disposable ones.

FIG. 6 shows in cross section the coaxial structure 10, implying that it can take the forms 11, 12, 13 etc simply placed on a road for example, on the part 101, and fixed by an adhesive strip 71, for example chosen by adhesive tapes based on special polymers for pavement. The strip is preferably arranged over the entire length L of the coaxial structure 10.

FIG. 5 shows in cross section a coaxial structure 10 first threaded into a profile 70 or into a tube of elastic synthetic material which does not obstruct the radial vibrations to be transmitted to the structure 10. The profile 70 is preferably applied to any the length L of the structure 10, and the assembly is held on the roadway by an adhesive strip 71.

Apart from these two examples of fixing, the structures 10 can be simply bonded to the road, for example by means of resins which polymerize very quickly at room temperature. Indeed, we recall that the structures 10 have a very small diameter, less than or equal to 3 mm; they are therefore easy to fix.

The lifetime of the detector on the road largely depends on the principle adopted for the fixing. It is sometimes sought to make the structures 10 as visible as possible to avoid sabotage. In this case the method illustrated in Figure 6 seems the most suitable.

It is obvious that it is also possible, for a longer service life, to bury the structures 10. They will not then have the advantage of rapid installation but will retain the other qualities listed in points a) to e).

With the structures according to the invention, it is also possible to realize all other applications, such as the weighing of vehicles for example.

Claims (10)

1. An axle detector for installation on the surface of a multi-lane road, including at least a piezoelectric coaxial cable (1, 2, 3, 4) which comprises a central conductor (1), a metallic cladding (2) and a filler material (3, 4) between the cladding (2) and the conductor (1), characterized in that the piezoelectric coaxial cable (1, 2, 3, 4) comprises at least one region which is referred to as the active region in which the filler material (3) is of a piezoelectric type, and at least one adjoining region which is referred to as the neutral region and in which the filler material (4) is neither piezoelectric nor potentially piezoelectric.
2. A detector as claimed in Claim 1, characterized in that for the monitoring of the M^th lane of an N-lane road, where 1 ≦ M ≦ N, the detector comprises a coaxial cable having an active region (A) whose length equals the transverse dimension of the lane to be monitored, and also comprises an adjoining neutral region (B-E) whose length at least equals the overall transverse dimension of the remaining M-1 other lanes.
3. A detector as claimed in Claim 1, characterized in that for the monitoring of each of the N lanes of a road, it comprises N coaxial cables (11-15) as claimed in Claim 2, each of said cables being defined by a different parameter M, where 1 ≦ M ≦ N.
4. A detector as claimed in any one of the Claims 1 to 3, characterized in that the cable (cables) also has (have) a neutral part at one of its (their) ends, which neutral part comprises a coaxial connection system for connecting the detector to a data processing device (110).
5. A detector as claimed in Claim 4, characterized in that the connection system (21-25) comprises a coaxial connector and a coaxial cable for connection to the data processing device (110).
6. A detector as claimed in any one of the preceding Claims, characterized in that in the piezoelectric coaxial cable (cables) the filler material of the active region is formed by a powdery piezoelectric ceramic material, the filler material of the adjoining neutral region or of the end being a powdery insulating mineral.
7. A detector as claimed in Claim 6, characterized in that the powdery piezoelectric ceramic material is chosen from a mixture of titanate and lead zirconate or barium titanate doped with lead titanate, and in that the powdery insulating mineral is chosen from magnesium (MgO) or silicon (SiO₂) or alumina (Al₂O₃) or a mixture of several insulating minerals containing inter alia one of these powders.
8. The use of a detector as claimed in any one of the Claims 2 or 4 to 7 in as far as the latter are dependent on Claim 2, for selectively monitoring the M^th lane of an N-lane road.
9. The use of a detector as claimed in any one of the Claims 3 or 4 to 7, in as far as the latter are dependent on Claim 3, for monitoring all lanes of an N-lane road.
10. The use of a detector as claimed in any one of the Claims 8 or 9, characterized in that the detector is connected to a data processing device (110), arranged on the shoulder of the road or on the central reservation, by way of a connection system connected to the end of the neutral part of the piezoelectric coaxial cable (cables), in that the cable (cables) is (are) arranged across the surface of the road, in that the active part (A) of each cable covers one lane while the neutral part (B-E) covers the other lanes between the active part and the zone without road traffic in which the data processing device is arranged, and in that the connection system between the coaxial piezoelectric cable (cables) and the data processing device (110) is also installed in said zone without road traffic.

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